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Why does it seem forecasters always predict an above-average hurricane season?

NOAA’s latest outlook predicts busy Atlantic Hurricane Season

Above-average Atlantic hurricane season forecast by the National Hurricane Center
Above-average Atlantic hurricane season forecast by the National Hurricane Center

ORLANDO, Fla.- – Here’s the thing about hurricane season. It can be a really active year in the sense we get all the way to the end of the alphabet, but none of them actually impact land/people and therefore it is perceived as a quiet season. On the other hand, it can be a really slow season, but that one catastrophic storm comes ashore and changes life forever.

Take the 1992 hurricane season for example. In terms of named storms, there were 7. The average number of storms in a given season is 12. That year, A weak, unnamed subtropical storm developed in April, followed by a couple of tropical depressions that never intensified into named storms. It took until the middle of August to get the season’s first named storm. Unfortunately, that name was Andrew. The rest is history.

If it seems as if the National Oceanic and Atmospheric Administration has been predicting above average seasons a lot lately, you would mostly be correct! NOAA has, however, been extremely accurate in predicting seasonal storm activity.

Four out of the last five years they hit the nail on the head. Last year a few more storms developed than originally anticipated, but a higher storm count was forecast in their mid-season update in August.

NOAA pre-season outlooks vs. what actually occurred. The average number of storms in a season is 12. The last 4 years have been above average. In 2016, 2018 and 2019, NOAA predicted a near-normal to above normal year. In 2017 an above normal season was predicted. In 2015 a below normal season was forecast.
NOAA pre-season outlooks vs. what actually occurred. The average number of storms in a season is 12. The last 4 years have been above average. In 2016, 2018 and 2019, NOAA predicted a near-normal to above normal year. In 2017 an above normal season was predicted. In 2015 a below normal season was forecast.

Thursday, NOAA released its outlook for the upcoming hurricane season and again is predicting a more active than normal season. Their forecast and driving factors leading to this particular season’s outlook are highlighted here. It is important to note that the forecast does not forecast landfall, just the number of storms.

There is more science involved as to why we have not only been seeing above-average forecasts of late, but more often than not, above average seasons as well.

Similar to El-Nino Southern Oscillation or ENSO, the periodic fluctuation in sea surface temperatures across the equatorial Pacific Ocean, the Atlantic Multidecadal Oscillation, AMO rules the roost in the Atlantic Basin. ENSO typically has a period of 7 years give or take. For example El-Nino will be present for about 7 years and then it will be La-Nina’s turn.

The AMO has a cycle that is much longer, on the order of 20-40 years. The AMO entered into its warm phase, warmer than normal sea surface temperatures in the Atlantic, in 1995. There won’t be a quiz, but it is important to note warmer ocean temperatures have been around since the mid 90s do in part to a natural climate cycle.

Since then, the Atlantic has been in an era of active hurricane seasons, some extremely active. Previous to the mid 90s, the AMO was in its warm phase from the 30s to mid 60s. The 1950s were known for their active hurricane seasons and part of another active era.

Other weather factors come into play that can help to enhance or suppress the overall active era, which is why every season isn’t above normal even in this active era.

The moral of the story? Be prepared. Even if the prediction was for one named storm. If that storm impacted you, you would consider it a busy season. Here’s to hoping they all stay out at sea.


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